Any firm idea of when these two things were done to our model kits?
I've been building since the late 50's (steady through to the late 60's) and I can honestly saw I absolutely do not remember!!!
I do remember opening boxes in the stores and looking inside but I can't say that they came that way or someone unwrapped it.
Once inside the box I again do dont recall if the parts were loose or in bags.
An exception would be the Lindberg kits that had motors. The motor parts were in a small cellophane bag. One other would be the Atomic Power Plant definitely had loose sprues or were kinda wrapped with cheap tissue-like paper.